Proline is repeated in the center of proteins found in tooth enamel. When the repeats are long, such as in humans, they contract groups of molecules that help enamel crystals grow. When the repeats are short, such as in frogs, teeth don't have the enamel prisms that provide strength, the researchers explained.

The research offers clues on how to engineer tooth enamel.

"We hope that one day, these findings will help people replace lost parts of the tooth with a healthy layer of new enamel," lead researcher Tom Diekwisch, professor and head of oral biology at the University of Illinois at Chicago College of Dentistry, said in a news release.

But the benefits may extend well beyond teeth.

"Proline repeats are amazing. They hold the key to understanding the structure and function of many natural proteins, including mucins, antifreeze proteins, Alzheimer's amyloid and prion proteins," Diekwisch said. "We hope that our findings will help many other important areas of scientific research, including the treatment of neurodegenerative diseases."

The findings are published in the Dec. 21 online edition of the journal PLoS Biology.